Chelsea have been a revelation ever since Roman Abramovich took over the club in 2003. The Blues have seen a lot of success in the last two decades and look strong going forward.The London club have had some fantastic players at their disposal, some of whom have gone on to become world-class. The likes of Didier Drogba, Frank Lampard, John Terry, Petr Cech and many others have played for Chelsea and done wonders for the club.Some world-class footballers regret leaving ChelseaThe Blues have had some demanding managers over the years and with those managers came world-class players. That being said, not every top player decided to settle permanently with Chelsea.Some of them went away from London and found success. However, few of the players regretted leaving Chelsea as well. On that note, let's have a look at those top players who should not have left the Blues:#5 Joe ColeChelsea v Everton - Premier LeagueGraduating from the West Ham United academy, Joe Cole was considered one of the hot young prospects during his young days. Manchester United were very keen on signing the Englishman when he was just 16.Buaksib@buaksibJoe Cole stats for @ChelseaFC (career-wise)🏃 281 Appearances;⚽ 40 Goals;🅰 42 Assists.#JoeCole #ChelseaFC #WestHam #LiverpoolFC #Lille #AstonVilla #England4:33 PM · Mar 23, 2021Joe Cole stats for @ChelseaFC (career-wise)🏃 281 Appearances;⚽ 40 Goals;🅰 42 Assists.#JoeCole #ChelseaFC #WestHam #LiverpoolFC #Lille #AstonVilla #England https://t.co/VKWkh63oreEventually Joe Cole developed with the Hammers before moving to Chelsea in the summer of 2003, becoming the sixth signing since Roman Abramovich's takeover. He was touted as the ideal replacement for the great Gianfranco Zola. With his flair, agility and amazing dribbling skills, the English midfielder was a delight to watch for the Blues. Speaking about his departure from Stamford Bridge, Cole stated:I’d have taken any money they’d have given me because I didn’t want to leave. It was hard for me to leave the club at the time. It was difficult."He won three Premier League titles with Chelsea before his contract expired in 2010 after which he signed for Liverpool. The struggle to renew his contract led to his departure, which Cole deeply regrets till date as his move to Merseyside was a big flop.#4 Michael BallackChelsea v Portsmouth - FA Cup FinalThe German was a very smart operator and one of the most technically gifted midfielders of his generation. With some amazing performances for both Bayer Leverkusen and Bayern Munich in the Bundesliga, Michael Ballack impressed many.Vince™@Blue_FootyMichael Ballack: "I think the Chelsea team during my time at the club deserved to win more titles, especially outside England, but I never regret moving there, and if time comes back I will still choose the same path that I enjoyed."01:03 AM · Sep 10, 20203748275Michael Ballack: "I think the Chelsea team during my time at the club deserved to win more titles, especially outside England, but I never regret moving there, and if time comes back I will still choose the same path that I enjoyed." https://t.co/MWoYTaVaFfThis helped him earn a move to Chelsea in 2006 on a free transfer. Over time, the German maestro became a key member of the Blues. He won the Premier League with them and brought a lot of composure and intellect in the Blues' midfield. Enjoying his football in London, Ballack wanted to retire at Chelsea. He opened up on the whole episode and revealed:"Carlo wanted me [to stay] but the club made a decision to only give players of that age a one-year contract. I wanted two. Today, I can say maybe it was wrong. I should have stayed, even for that one year."But the Premier League club offered a one-year contract instead of the expected two and therefore Ballack decided to return to Bayer Leverkusen in 2010. He spent two years at the German club before retiring despite hoping that he would be playing in the final days of his career at Chelsea.